Effect of HCl additions on forced hydrolysis of FeCl3 solutions

Abstract

The effect of HCl additions on the formation of precipitates by hydrolysis of FeCl3 solutions at 90 °C has been investigated using X-ray powder diffraction (XRD), FT-IR spectroscopy and transmission electron microscopy (TEM). In the precipitation systems with 0.1 M FeCl3, the concentration of HCl varied between 0.005 and 0.1 M, whereas the maximum time of hydrolysis was 35 days. At the beginning of the hydrolytic process, the formation of precipitate was strongly suppressed with an increase in HCl concentration. β-FeOOH was found as a single phase in the precipitates for the concentration 0.1 M FeCl3+0.01 M HCl after 1 and 3 days of hydrolysis. For the concentrations [HCl]≥0.05 M, the precipitates also contained a small amount of α-FeOOH. FT-IR spectroscopy was proved to be a useful technique in the detection of α-FeOOH. After 35 days of hydrolytic process, α-Fe2O3 was found as the end product of precipitation, whereas some precipitates also contained small amounts or traces of α-FeOOH. The size and shape of the particles strongly depended on the HCl concentration. Forced hydrolysis of 0.01 M FeCl3+0.005 M HCl solution for 35 days yielded small and uniform α-Fe2O3 particles (∼0.08 μm).